SAXS and WAXD study of periodical structure for polyacrylonitrile fiber during coagulation

Small angle X‐ray scattering (SAXS) and wide angle X‐ray diffraction (WAXD) were adopted to investigate the formation and development of high order structure within polyacrylonitrile (PAN) precursor during coagulation. The scattering signal came from the microvoids and long period structure was separated reasonably by the analog computation method of decomposition of the one‐dimensional profile. Based on the established methodology, the statistic parameters of long period structure, such as length of the long period structure, crystalline region and amorphous region, were obtained by the analysis of correlation function. The results indicated that during the coagulation, the length of long period of the nascent coagulated fiber was 56.1 nm (meridional direction) and 35.6 nm (equatorial direction), respectively. The evolution of the long period during the coagulation was also discussed by combining WAXD data. With the processing of coagulation, the long period was decreased since the crystallinity increased. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and orientation study of a magnetically aligned liquid‐crystalline chitin/poly(acrylic acid) composite

A high magnetic field of 5 T was used to fabricate a magnetically aligned, optically anisotropic, liquid‐crystalline chitin/poly(acrylic acid) composite. The aligned mesophase was fixed by photoinitiated free‐radical polymerization. From an examination of polarized optical micrographs and an X‐ray diffraction study, a high degree of orientation of 0.70 was observed for the composite with a higher liquid‐crystalline chitin concentration (10.70 wt %); the orientation was reduced with a decreased chitin concentration at a given acrylic acid concentration. The X‐ray data for the developed composite showed a uniplanar orientation for the chitin crystallites, with its molecular long axes perpendicular to the direction of the magnetic field. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 711–714, 2003     

Electronic structure and properties of camphorimine Cu(I) coordination polymers

The first Cu(I) coordination polymer with an aromatic‐substituted camphorimine ligand [(CuCl)(μ‐Cl) (Cu(H₂NC₆H₄NC₁₀H₁₄O)]_n was obtained from reaction of CuCl with 3‐(4‐aminophenylimino)‐1,7,7‐trimethylbicyclo[2.2.1]heptan‐2‐one (H₂NC₆H₄NC₁₀H₁₄O). The electronic and the surface properties (studied by X‐ray photoelectron spectroscopy) are consistent with two distinct coordination environments for the copper(I) atoms—tetrahedral and linear—for the polymer family [(CuCl)(μ‐Cl){Cu(YNC₁₀H₁₄O)}]_n. DFT band calculations reveal that the highest energy bands are more localized on the copper(I) tetrahedral sites than on the copper(I) linear sites. The redox properties of [(CuCl)(μ‐Cl){Cu(YNC₁₀H₁₄O)}]_n [Y = NMe₂ ( 2b ), NH₂, and H₂NC₆H₄NC₁₀H₁₄O ( 2a )] studied by cyclic voltammetry show that the oxidation potentials of the two copper centers are in fact indistinguishable. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis,characterization and single crystal structure determination of aluminum alkoxydisilanolates: precursors for silica–alumina composite

Several novel aluminum alkoxydisilanolate complexes were prepared by reaction of triphenylsilanol with aluminum 2‐methoxyethoxide, aluminum 2‐ethoxyethoxide, aluminum sec‐butoxide and aluminum iso‐propoxide. All new complexes, [(Ph₃SiO)₂Al(OR)]₂ [where R = CH₂CH₂OCH₃ (1), CH₂CH₂OC₂H₅ (2), CH(CH₃)CH₂CH₃ (3) and CH(CH₃)₂ (4)] were characterized by elemental analysis, mass spectrometry and infrared spectroscopy (IR), as well as ¹H, ¹³C, ²⁹Si and ²⁷Al NMR spectroscopies. The solid‐state structures of the representative compound 2 and 4 were also verified by single‐crystal X‐ray analyses. Complexes 2 and 4 are dimers having distorted trigonal bipyramidal and tetrahedral coordination at the aluminum center, respectively. The ²⁷Al NMR spectrum of compound 2 showed that the solid‐state structure of the complex was not retained in solution, and tetracoordinated aluminum was found in solution in contrast to the pentacoordinated geometry in the solid state. The hydrothermal treatment of 1 and 4 at 200 °C and the subsequent calcination at 1000 °C resulted in the formation of alumina–silica composite (4SiO₂·Al₂O₃) with γ‐alumina in the silica matrix. Copyright © 2010 John Wiley & Sons, Ltd.     

Relation between stress and segmental orientation during mechanical cycling of a natural rubber‐based compound

X‐ray diffraction technique is used to evaluate the evolution of the segmental orientation in a natural rubber sample during mechanical uniaxial stretching and in the Gaussian regime condition. The method proves to be sensitive enough for testing the validity of the stress‐optical law. Measurements are performed at different temperatures and show that the dependence of the orientation parameter upon elongation is very close to the prediction of classical phantom theories. On the contrary, a significant Mooney–Rivlin correction is needed to account for the stress–strain relation. Consequently, systematic deviations from the stress‐optical law are observed, in particular for elongations below 2. These deviations are adverse from predictions of both the constrained and the diffuse junction theories. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 943–950     

An analysis of deformation process on poly‐p‐phenylenebenzobisoxazole fiber and a structural study of the new high‐modulus type PBO HM+ fiber

This study is concerned with fiber structure of new high‐modulus type PBO fiber. Crystal modulus and molecular orientation change with stress was surveyed. Standard‐modulus type PBO (AS) fiber has hysteresis effect to applied stress while high‐modulus type PBO (HM) fiber shows reversible change. In order to raise actual PBO fiber modulus higher, nonaqueous coagulation process was adopted with conventional heat treatment. The fiber (HM+) so made gives 360 GPa in the Young's modulus and an absence of small‐angle X‐ray scattering pattern that is characteristic for aqueous‐coagulated PBO fiber with heat treatment (Zylon™ HM). The crystal structure form and crystal size for the HM+ fiber are the same as those of the HM fiber. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1605–1611, 2000     

Deformation mechanisms in uniaxial‐oriented semi‐crystalline PET‐films as a function of orientation to tensile direction

Poly(ethylene terephthalate) films with oriented lamellar structure were deformed in tensile experiments and investigated in situ using small angle X‐ray scattering. The tensile direction was set parallel, normal and in an angle of 45° relative to the surface normal of the lamellae. Data were interpreted in terms of two‐dimensional autocorrelation functions. The deformation of lattice spacing and lamellar orientation can largely be explained by affine transformations. The sample, where the lamellar surface normal was normal to tensile direction, developed a chequerboard type arrangement of crystalline parts. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 159–169     

Effect of organic solvent on the crystal structure of Concanavalin A

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Structural origin for the strain rate dependence of mechanical response of fluoroelastomer F2314

The structural evolution of fluoroelastomer F2314 is studied during uniaxial tensile in a large strain rate range (0.1–150 s^?1) with the combination of a homemade high‐speed stretching device and in situ small‐ and wide‐angle X‐ray scattering techniques. Based on the mechanical behaviors and structural evolutions, three strain rate regions (I–III) are defined. The microphase‐separated structure plays an important role in the mechanical response of F2314. In Region I, deformation of soft domains is the main process before yielding, accompanied by the destruction of lamellar crystals in hard domains. In the stress plateau zone, deformation of hard domains is confirmed as the primary mechanism of energy dissipation. With the orientation parameter of the amorphous phase reaching a critical value, strain hardening is triggered. Recrystallization also takes place in strain hardening zone. In Region II, due to the mismatch between the mobility of molecular chains in hard domains and the acting time of stress, large deformation of hard domains is more and more difficult to occur with the disappearance of recrystallization. In Region III, as almost all molecular chains have no time to adjust or relax to fit the stress field, the sample presents a brittle fracture. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 607–620     

Atmospheric pressure deposition of fluorine‐doped SnO2 thin films from organotin fluorocarboxylate precursors

Nine organotin fluorocarboxylates R_nSnO₂CR_f (n = 3, R = Bu, R_f = CF₃, C₂F₅, C₃F₇, C₇F₁₅; R = Et, R_f = CF₃, C₂F₅; R = Me, R_f = C₂F₅; n = 2, R = Me, R_f = CF₃) have been synthesized; key examples have been used to deposit fluorine‐doped SnO₂ thin films by atmospheric pressure chemical vapour deposition. Et₃SnO₂CC₂F₅, in particular, gives high‐quality films with fast deposition rates despite adopting a polymeric, carboxylate‐bridged structure in the solid state, as determined by X‐ray crystallography. Gas‐phase electron diffraction on the model compound Me₃SnO₂CC₂F₅ shows that accessible conformations do not allow contact between tin and fluorine, and that direct transfer is therefore unlikely to be part of the mechanism for fluorine incorporation in SnO₂ films. The structure of Me₂Sn(O₂CCF₃)₂(H₂O) has also been determined and adopts a trans‐Me₂SnO₃ coordination sphere about tin in which each carboxylate group is monodentate. Copyright © 2005 John Wiley & Sons, Ltd.     

Effect of postcasting heat‐treatment on the structure and properties of semicrystalline phase‐inversion poly(vinylidene fluoride) membranes

Microporous PVDF membranes were prepared by immersion‐precipitation in 1‐octanol of casting dopes dissolved at different temperatures, with dissolution temperature affecting strongly the membrane microstructure. The effect of postcoagulation thermal annealing, which is an additional thermal parameter, on membrane microstructure and properties is probed herein. Membranes obtained were annealed at temperatures up to 160 °C, which is close to the melting point of PVDF polymer. Annealing leads to a substantial modification of the nano‐scale fine structure of the membranes, while the overall‐microporous structure is preserved. At elevated annealing temperatures, nano‐grains, fibrils, and stick‐like crystalline entities gradually eclipse, while globules develop more robust connections based on wide bands of crystal elements. Probing by X‐ray diffraction and dynamic scanning calorimetry shows that crystallinity increases when annealing temperature and time are increased. As regards mechanical properties, the tensile strength of the membranes can be enhanced substantially, up to about 10 times, upon appropriate high temperature prolonged annealing. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1880–1893, 2009     

Comparative study on the effect of precursors on the morphology and electronic properties of CdS nanoparticles

Cadmium dithiocarbamate and cadmium ethyl xanthate complexes were synthesized and characterized by microanalysis, Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric analyses. The complexes were employed as molecular precursors for the fabrication of CdS nanoparticles in hexadecylamine (HDA) and oleylamine (OLA) at a temperature of 250 °C. Spherical and oval shaped particles with sizes ranging from 9.93 ± 1.89 to 16.74 ± 2.78 nm were obtained in OLA while spherical, oval and rod shaped particles with sizes ranging from 9.40 ± 1.65 to 29.90 ± 5.32 nm were obtained in HDA. Optical properties of the nanoparticles showed blue shifts as compared to the bulk CdS, with the OLA capped nanoparticles slightly more blue shifted than the corresponding HDA capped nanoparticles. Results of crystallinity patterns revealed hexagonal phase of CdS.     

Synthesis,spectroscopic and X‐ray single‐crystal structure study of bis(2‐methoxy‐ethanolato)‐bis(8‐quinolinato)titanium(IV)

Reaction of Ti(OCH₂CH₂OR)₄ (R?CH₃ and C₂H₅) with 8‐hydroxyquinoline in benzene at room temperature resulted in the formation of Ti(C₉H₆NO)₂(OCH₂CH₂OR)₂, characterized by IR, ¹H‐NMR, UV and mass spectroscopies. The molecular structure of Ti(C₉H₆NO)₂(OCH₂CH₂OCH₃)₂ has been determined by single‐crystal X‐ray structure analysis. The geometry at titanium is a distorted octahedron, with the nitrogen atoms of quinolinate occupying the trans position with respect to oxygens of the 2‐methoxyethoxy groups. The prepared quinolinate derivatives of titanium alkoxides are very stable towards hydrolysis and harsh conditions are required for hydrolytic cleavage. Copyright © 2005 John Wiley & Sons, Ltd.     

Functionalized carbon nanotube/polyacrylonitrile composite nanofibers: fabrication and properties

The functionalized multi‐walled carbon nanotubes (f‐MWCNTs) were obtained by Friedel–Crafts acylation, which introduced aromatic amine groups onto the sidewall. And the grafted yield was adjusted by controlling the concentration of the catalyst. The composite solutions containing f‐MWCNTs and polyacrylonitrile (PAN) were then prepared by in‐situ or ex‐situ solution polymerization. The resulting solutions were electrospun into composite nanofibers. In the in‐situ polymerization, morphological observation revealed that f‐MWCNTs was uniformly dispersed along the axes of the nanofibers and increased interfacial adhesion between f‐MWCNTs and PAN. Furthermore, two kinds of f‐MWCNTs/PAN composite nanofibers had a higher degree of crystallization and a larger crystal size than PAN nanofibers had, so the specific tensile strengths and modulus of the composite nanofibers were enhanced. And the thermal stability of f‐MWCNTs/PAN from in‐situ method was higher than that of ex‐situ system. When the f‐MWCNTs content was less than 1 wt%, the specific tensile strengths and modulus of nanofibers were enhanced with increase in the amounts of f‐MWCNTs, and f‐MWCNTs/PAN of in‐situ system provided better mechanical properties than that of ex‐situ system. Copyright © 2010 John Wiley & Sons, Ltd.     

A kinetically stabilized ferrocenyl diphosphene: synthesis, structure, properties, and redox behavior

A new, stable ferrocenyl diphosphene [Tbt-P==P-Fc] (1) (Tbt=2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Fc = ferrocenyl) was synthesized by the dehydrochlorination reaction of the corresponding diphosphane, [Tbt-P(H)-P(Cl)-Fc] (8), with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in good yield. Diphosphene 1 is very stable in the solid state and also in solution. In the 31P NMR spectrum (C6D6), diphosphene 1 showed a low-fielded AB quartet at delta 501.7 and 479.5 ppm with the coupling constant 1J(PP)=546 Hz, which is characteristic of an unsymmetrically substituted trans-diphosphene. The molecular structure of 1 was established by X-ray crystallographic analysis, which showed a trans-diphosphene with a C-P-P-C torsion angle of 177.86(17) degrees . The phosphorus-phosphorus bond length of 1 [2.0285(15) A] which is considerably shorter than the typical P-P single-bond lengths (ca. 2.22-2.24 A) and within the range of reported P=P double-bond lengths (1.985-2.051 A) for diaryl diphosphenes, evidenced the P=P double-bond character of 1 in the solid state. In addition, the cyclic voltammograms of 1 showed reversible reduction and oxidation couples at -1.95 and +0.34 V versus SCE, respectively. The electrochemical results for 1 were reasonably supported by the DFT calculations, which suggested that the LUMO and HOMO orbitals should be mainly pi* orbital of the diphosphene moiety and d orbitals of the iron(II) atom, respectively.